It depends (Big 10). This has been allowed rarely for the non-science classes so long as it doesn't interfere with the P1 schedule (so US Government or American History for the ones who did not get the prerequisites in the US and is a university requirement for all degrees at my place), but I doubt most Admission Committees would entertain one for any sciences prerequisite. Usually, admission is contingent on finishing prerequisites by the start of the fall.
And no, they cannot "waive" but can substitute due to Regional Accreditation going after them. There are flexibility to the standards, but the overall credit standard is usually something that's approved at the university and not the college level.
That said, I wouldn't want to load my P1 year with anything else except for athletics or fine arts courses. It's not necessary a tough year, but it is a busy one.